Toxicology is the field that studies poisons, especially how poisons work and how to treat them. If you’re writing a true crime story, you should study toxicology to know what happens when the villain poisons the victim’s tea. Mwah ha ha.
Have you ever seen a label that said "toxic"? That means that substance will harm you. Toxicology — which is a branch of pharmacology — has to do with toxic substances (poisons). It comes from the Greek word for “arrow poison.” Not all poisons come at the end of an arrow, though. If a toxicology report is done on a dead person, it will reveal if they had any dangerous substances in them, such as illegal drugs or drain cleaner.